Variable power supply



2 Sheets-Sheet 1 A. B. ELLIOTT, JR

VARIABLE POWER SUPPLY June 13, 1967 Filed Dec. 17, 1962 June 13, 1967 A.B. El l |o'rr, JR

VARIABLE POWER SUPPLY 2 Sheets-Sheet 2 Filed DSC. 17, 1962 United StatesPatent O 3,325,682 VARIABLE POWER SUPPLY Andrew Byron Elliott, Jr.,River Forest, El., assigner to Jefferson Electric Company, Bellwood,Ill., a corporation of Delaware Filed Dec. 17, 1962, Ser. No. 245,227 7Claims. (Cl. 315-97) This invention relates to a variable power supplyfor gaseous discharge devices, and in particular for uorescent lamps ofthe continuously heated ilament type, otherwise known as rapid startlamps.

It has been proposed to control the luminosity of a gaseous dischargedevice by regulating the power supplied to the arc by means of a phasecontrol device connected in series with the arc. However, such phasecontrol arrangements cannot satisfactorily be applied to a solid statecircuit due to the irregular voltage wave shape developed across thecontrol device due to larnp operation, which produces discontinuities inthe response and consequently results in a jump dimming action.

It is an object of my invention to provide a solid state dimmingarrangement which has an exceedingly wide range of variation between thepoints of minimum and maximum luminosity.

Another object of my invention is to provide an arrangement whichpermit-s smooth dimming, in the sense that sudden jumps in or incrementsot luminosity are avoided as the cont-rol is operated from dim to brightor vice versa.

According to my invention I provide a solid state phase control devicein which that which is controlled is the sinusoidal voltage of thesupply line, thus providing an improved and less costly variable powersupply, as compared with prior art arrangements.

Another object of my invention is to provide an improved variable powersupply which includes a ballast suitable for operating rapid startlamps.

The characteristic of rapid start lamps is that two sources of power arerequired, one for energizing the arc, and one for energizing thefilaments. In the usual ballast, the arc and the filaments arecustomarily energized from a common primary winding by means of separatesecondary circuits, the one for energizing the arc being known as theoperating circuit, and those for energizing the larnents 'being known asthe filament circuits.

The present invention provides a supply line type of phase control forenergizing the arc while at the same time the power supplied to the lamplaments is constant.

Another object is to provide an improved dimming `arrangement which willignite the lamps at the point of lowest luminosity. In other words, thelamps do not have to be ignited at a point of high luminosity and thenthe control turned down to a low luminosity point.

A still further object is to provide a variable power supply which isoperative for uniformly controlling the luminosity of a great number oflamps, to the end that a single rheostat or dimmer control mechanism canbe utilized to control all of the ballasts of a particular installation,irrespective of whether the ballasts comprise a single branch circuit ora number of branch circuits.

With reference now to the drawings in which like reference numeralsdesignate like parts:

FIG. l is a circuit diagram showing a preferred embodiment of myinvention;

FIG. 2 is a circuit diagram showing the bridge connection of the phasecontrol device shown in FIG. 1;

FIG. 3 shows a modified system;

FIG. 4 is a diagram of the phase control device of FIG. 3;

Patented June 13, 1967 FIG. 5 shows a modified type of phase controldevice; and

FIG. 6 shows a modiiied arc supply transformer.

In FIG. 1, leads 1G and 11 are provided for connection to a suitable ACsource, such as a 60 cycle, 118 volt line. Connected in parallel acrossthe leads 10 and 11 are a plurality of ballasts 12 for energizinggaseous discharge devices 13, such as fluorescent lamps.

Disposed in series circuit with all of the ballasts 12 is a phasecontrol device 14, this being connected in the lead 10 ahead of thefirst ballast 12.

Each ballast comprises an arc supply transformer 15 for energizing thelamp 13, and a lament transformer 16 for energizing the lamp filaments.

The arc supply transformer 15 is a high reactance transformer comprisinga primary winding 17 and a secondary winding 18 which are looselycoupled to each -other by a suitable core structure. For instance, asdiagrammatically shown with respect to one of the ballasts, the windings17 and 18 may be mounted in end to end relationship on a winding leg 19of a suitable core structure so as to provide a ilux leakage paththerebetween, the latter being designated by the conventional symbol 20.

The primary 17 is connected across the leads 10 and 11, the transformerhaving suitable output or secondary leads 21 and 22 across which thelamp 13 is connected to provide the operating circuit. The windings 17and 18 may either be isolated, or connected in autotransformerrelationship, as shown.

Thus the primaries 17 are connected in parallel with each other acrossthe leads 10 and 11, and in series circuit with the phase control device14.

The iilarnent transformer 16 is a tightly coupled transformer comprisinga primary winding 23 and two secondary windings 24 and 25, which areconnected by suitable conductors to the lament-s 24a and 25a of the lamp13.

A branch lead 26 is connected at point 27 to the lead 1li, the point 27being ahead of the phase control device 14. The primary windings 23 areeach connected Abetween the branch lead 26 and the lead 11, all of theprimaries 23 being connected in parallel relationship with each other.Thus the iilament transformers 16 are not affected by the operation ofthe phase control device 14.

As shown in FIG. l, the phase control device 14 comprises a bridgenetwork 29 having a rectier diode 30 in each of its lfour legs, andhaving -a bridge connection 31 across the midpoint terminals 32 and 33.

The bridge connection 31 is shown in FIG. 2, and comprises an SCR(silicon controlled rectiiier) 34 having a gate 35.

A suitable trigger circuit is provided for the gate 35 of SCR 34, whichincludes a relaxation oscillator 36 connected in parallel with a zenerdiode 37 across junction points 38 and 39. A dropping resistor 4t) isconnected between point 38 and the terminal 32, and point 39 isconnected to terminal 33.

The relaxation oscillator 36 includes a unijunction transistor 41connected between points 38 and 39 and having a base-two 42, a `base-one43, and an emitter 44. The base-one 43 is connected to the lgate 35, andthe emitter 44 is connected to a junction point 45 in an RC chargingcircuit, the latter comprising series resistances 46-47 and a capacitor48.

The capacitor 48 is charged at -a rate determined by the seriesresistance 46-47. When the emitter bre-ak-over voltage is reached, thecondenser 48 discharges through a resistance 49 which is connectedbetween the ybase-one, 43 and the junction point 39. Thus, a pulse is-applied to the gate 35 which is positive with respect to the cathode ofthe SCR and triggers the SCR into a conductive state.

As an example of suitable quantities, the Zener 37 may lbe a 22 voltZener, and the dropping resistor 40 may be 18,000 ohms. A 330 ohmresistance 50 is connected between the base-two 42 and the junctionpoint 38. The resistance 49 is 47 ohms. Also, -a 10,000 ohm resistance,not shown, may preferably be connected in parallel across the Zener 37to dampen the rate of voltage buildup with respect to the referencepoint 3S. In the RC charging circuit, the resistance 46 may be 3000ohms, the resistance 47 may be a 70,000 ohm variable resistance, and thecondenser 48 is .12 mfd.

Regulation of the variable resistance 47 controls the point in each halfcycle at which the SCR 34 switches from the blocking to the conductingstate, and thus controls the area under the wattage half cycle curve.

In operation, the power which is supplied to the operating circuit iscontrolled by regulation of the variable lresistance 47 of the phasecontrol device 14, with the result that the luminosity of the lamps 13may be regulated. Howe-ver, such regulation does not affect the powersupplied to the lamp filaments 24a and 25a with the result that theminimum arc sustaining voltage is not increased over the rated operatingvoltage of the lamp.

The arrangement shown has been found to supply adequate voltage in theoperating circuit for operating the lamps at all degrees of luminosity.Since the power supply to the lamp filaments is not reduced by theoperation of the phase control device, it is possible to start the lampsat almost the point of lowest luminosity.

One advantage of placing the phase control device in the primary circuitis that lower voltage components can be used than when placed in thesecondary circuit, thus reducing materially the cost of the phasecontrol device.

A further advantage of the present arrangement is that the operation ofthe trigger means is not adversely affected by the irregular voltagewave shape of the operating circuit for the reason that the triggercircuit draws on the line voltage which is substantially sinusoidal.According to the FIG. 2 embodiment the supply voltage for the triggercircuit is the voltage which is developed across the SCR duringblocking, land this is the line voltage.

FIG. 3 shows a multple branch circuit installation, in which each of thebranch circuits A, B and C are substantially identical to the circuit ofFIG.L 1, except for the phase control device 14. Here the various leads16 and 11 are connected to a common pair of supply leads 8 and 9.

The phase control device 14', as shown in FIG. 4, is a bridge typedevice similar to that shown in FIG. 1 having an `SCR 34 connectedacross the midpoint terminals 32' and 33. However, in the FIG. 4embodiment, a single trigger device 52 is provided for all of the SCRs34', the coupling being by means of 4suitable pulse transformers 51. Asshown in FIG. 4, the secondary of the pulse transformer 51 is connectedacross the gate 35 and the terminal 33. The primary of the pulsetransformer 51 is connected to the trigger device S2 by suitable leads53, the various primaries being connected in parallel.

The trigger device 52 is energized from the common supply lead lines 8and 9, and the connection therewith provides suitable means by which thetrigger device 52 is synchronized to the proper phase relationship withrespect to the supply voltage. Thus all of the branch circuits A, B, andC may be controlled by a suitable variable resistance located in thetrigger device 52.

A modified form of phase control device 14 is shown in FIG. 5. Thiscomprises two SCRs 55 and 56 connected in back to back .relationship andbeing interposed in the lead 10. The gates of the SCRs 55 and 56 areseparately triggered by a pulse transformer 57, the two secondaries lS,59 of which are connected between the gate and cathode of each SCR, andthe :primary 60 of which may be energized by a suitable trigger device52.

Although only a single lamp ballast 12 is shown, it will be understoodthat a two or three lamp ballast may be substituted Ltherefor ifdesired. For example, a suitable arc supply transformer 15 for Va twolamp ballast is shown in FIG. 6, in which two secondaries 61 and 62 areprovided, each being connected in series with the primary winding 17 andbeing in parallel connection with each other, and adapted for energizingtwo lamps, 63 and 64.

In some installations, it may be preferred to'provide a phase controldevice 14' for each Iballast 12, in which event, the two can be enclosedin a single housing 65, as shown with respect to branch circuit C inFIG. 3, vall of the combined units being controlled from the commontrigger device 52.

Although only lprefered embodiments of my invention have been shown anddescribed herein, it will be understood that various modifications andchanges may be made -in the constructions shown without departing fromthe spirit of my invention as pointed out in the appended claims.

I claim:

1. Variable power supply means for starting and operating a plurality offilament type gaseous discharge devices comprising first and secondpower leads for making a connection to an alternating current source, aplurality of ballasts each including a high reactance :arc supplytransformer and a filament transformeneach of said high reactance arcsupply transformers comprising a primary winding and a secondarywinding, all of said primary windings being connected in parallel acrosssaid first and second power leads, a phase control device connected insaid first power lead between said primary windings and said alternatingcurrent source, a branch power lead connected to said first power leadat a point between said phase control device and said alternatingcurrent source, said filament transformers each including a primarywinding and a plurality of secondary windings, the primary windings ofeach of said lament transformers being connected in parallel across saidbranch power lead and said second power lead, output lead means for eachof said arc supply transformers, each of said output lead means beingconnected to the secondary lwindings of its associated arc supplytransformer and having outer ends for making a connection across atleast one gaseous discharge device, and output lead means for each ofthe secondary windings of each of the filament transformers connected atone end to said secondary windings, and hav-ing outer ends for making aconnection with the yfilaments of said gaseous discharge devices.

2. Variable power supply means as claimed in claim- 1 in which saidphase control device comprisesva full wave rectifier bridge networkproviding midpoint terminals, and a silicon controlled rectifierconnected across said midpoint terminals, and a trigger device foractuating the gate of said silicon controlled rectifier.

3. Variable power supply means as claimed in claim 2 in which saidtrigger device is connected across said midpoint terminals.

4. Variable power supply means as claimed in claim 2 in which saidtrigger device is connected across said rst and second power leads at apoint between said phase control device and said alternating'currentsource.

5. Variable power supply means as claimed in claim 1 in which said phasecontrol device comprises Va pair of silicon controlled rectifiersconnected back to back, and trigger means for actuating the gates ofsaid silicon controlled rectifier.

6. Variable power Vsupply means for starting and operating a pluralityof filament type gaseous discharge devices comprising rst and secondpower leads for making a connection to an alternating current source, aplurality of ballasts each including a high reactance arc supplytransformer and a filament transformer, each of said high reactance arcsupply transformers comprising a primary winding and a secondarywinding, a phase control device for each of said ballasts, meansconnecting each phase control device in series circuit with itsassociated primary winding and across said first and second power leads,said filament transformers each including a primary winding and aplurality of secondary windings, the primary windings of each of saidfilament transformers lbeing connected in parallel across said first andsecond power leads, output leads means for each of said arc supplytransformers, each of said output lead means being connected to thesecondary winding of its associated arc supply transformer and havingouter ends for making a connection across at least one gaseous dischargedevice, a pair of output leads for each of the secondary windings ofeach of the lament transformers, connected at one end to said secondarywindings, and having outer ends for making a connection with thefilaments of said gaseous discharge devices, a common trigger devicehaving its output connected to each of said phase control devices, andhaving its input connected across said rst and second power leads.

7. Variable power supply means for energizing a lament type uorescentlamp comprising a ballast having a first core structure including awinding leg, primary and secondary windings mounted on said winding legin end to end relationship, said core structure and windings providing ahigh leakage reactance transformer, and lead means for connecting saidsecondary winding to a lilament type fluorescent lamp, a phase controldevice, means providing a series circuit adapted for energization by asource of alternating current and including said primary winding andsaid phase control device, said ballast also including a second corestructure having a primary Winding and a plurality of second windingsmounted thereon, lead means adapted for connecting each secondarywinding to a filament of said fluorescent lamp, and lead means forconnecting the primary winding of said ilament transformer to saidsource of alternating current.

References Cited UNITED STATES PATENTS 3,089,979 5/1963 Lovinger 315-97X 3,130,347 4/1964 Harpley 315-98 3,170,085 2/1965 Genuit 315-2273,205,404 9/1965 Kurata et al. 315-194 JOHN W. HUCKERT, PrimaryExaminer.

R. F. POLlSSACK, Assistant Examinez.

1. VARIABLE POWER SUPPLY MEANS FOR STARTING AND OPERATING A PLURALITY OFFILAMENT TYPE GASEOUS DISCHARGE DEVICES COMPRISING FIRST AND SECONDPOWER LEADS FOR MAKING A CONNECTION TO AN ALTERNATING CURRENT SOURCE, APLURALITY OF BALLASTS EACH INCLUDING A HIGH REACTANCE ARC SUPPLYTRANSFORMER AND A FILAMENT TRANSFORMER, EACH OF SAID HIGH REACTANCE ARCSUPPLY TRANSFORMERS COMPRISING A PRIMARY WINDING AND A SECONDARYWINDING, ALL OF SAID PRIMARY WINDINGS BEING CONNECTED IN PARALLEL ACROSSSAID FIRST AND SECOND POWER LEADS, A PHASE CONTROL DEVICE CONNECTED INSAID FIRST POWER LEAD BETWEEN SAID PRIMARY WINDINGS AND SAID ALTERNATINGCURRENT SOURCE, A BRANCH POWER LEAD CONNECTED TO SAID FIRST POWER LEADAT A POINT BETWEEN SAID PHASE CONTROL DEVICE AND SAID ALTERNATINGCURRENT SOURCE, SAID FILAMENT TRANSFORMERS EACH INCLUDING A PRIMARYWINDING AND A PLURALITY OF SECONDARY WINDINGS, THE PRIMARY WINDINGS OFEACH OF SAID FILAMENT TRANSFORMERS BEING CONNECTED IN PARALLEL ACROSSSAID BRANCH POWER LEAD AND SAID SECOND POWER LEAD, OUTPUT LEAD MEANS FOREACH OF SAID ARC SUPPLY TRANSFORMERS, EACH OF SAID OUTPUT LEAD MEANSBEING CONNECTED TO THE SECONDARY WINDINGS OF ITS ASSOCIATED ARC SUPPLYTRANSFORMER AND HAVING OUTER ENDS FOR MAKING A CONNECTION ACROSS ATLEAST ONE GASEOUS DISCHARGE DEVICE, AND OUTPUT LEAD MEANS FOR EACH OFTHE SECONDARY WINDINGS OF EACH OF THE FILAMENT TRANSFORMERS CONNECTED ATONE END TO SAID SECONDARY WINDINGS, AND HAVING OUTER ENDS FOR MAKING ACONNECTION WITH THE FILAMENTS OF SAID GASEOUS DISCHARGE DEVICES.